Very little is known in any organism concerning the genetic mechanisms by which ambient temperature effects biology. Due to plant sessile nature they must precisely measure ambient changes in temperature and respond accordingly, making them a model system in which to study the genetic mechanisms of temperature sensing. Temperature and light are critical environmental cues that orchestrate plant development and while understanding of light-mediated development (photomorphogenesis) has increased over the past decade very little is known about how a plant senses and integrates daily changes in ambient temperature (thermomorphogenesis). This study will utilize quantitative genetic techniques to describe the genetic architecture and extent of natural variation of thermomorphogenesis in the model flowering plant Arabidopsis. Thermomorphogenesis quantitative trait loci (QTL) will be mapped in a new set of recombinant inbred lines (RIL) and a global collection of Arabidopsis accessions. At least one gene associated with a QTL will be cloned and its role in thermomorphogenesis will be characterized. Furthermore, the relationship between natural variation at this gene and thermomorphogenesis in a global collection of Arabidopsis will be studied. Understanding the genetic basis of thermomorphogenesis will have broader scientific relevance not only for crops but in other non-plant organisms as well.